Preparation of substituted phosphide salts

ABSTRACT

Substituted sodium salts of phosphides are prepared by reacting a triarylphosphine with sodium in an aliphatic amine or diamine as a solvent or co-solvent. The resultant phosphides may be further treated with appropriate halides to produce unsymmetrical phosphines.

This application is the national phase of PCT/GB98/00909, nowWO98/43986.

The present invention relates to a process for preparing substitutedsodium salts of phosphides and use of such salts in preparingphosphines.

The preparation of alkali metal diarylphosphides and their subsequentconversion to unsymmetrical triarylphosphines is well-known in theliterature. Triarylphosphines are widely used as ligands to transitionmetals to afford useful catalysts for many different chemical reactions.Examples of these reactions, which are carried out on an industrialscale, include the hydroformylation reaction to produce aldehydes fromalkenes, the reaction of aryl halides or alkenes to produce esters andthe metathesis of simple alkenes to higher olefins. Althoughtriphenylphosphine is frequently used as such a ligand, betterspecificity is often encountered if unsymmetrical triarylphosphines ordiarylalkyl are used.

Methods which have been used to produce alkali metal diphenylphosphidesare low yielding, difficult to carry out on a large scale, and/orexpensive. For example, Hewertson and Watson (J. Chem. Soc. 1962. 1490)teach that sodium diphenylphosphide may be prepared in >75% yield by thecleavage of triphenylphosphine with sodium metal at −75° C. in liquidammonia. Whilst such reactions are common place in the laboratory, largescale production is hampered by the need of special (and very expensive)plant which can work at these low temperatures. Issleib and Frohlich (Z.Naturforsch, 1959, 14b, 349) have shown that the reaction may be carriedout with sodium metal in dioxane. However, in this case the yield isonly 25%. Clearly such a low yield is unacceptable for industrialproduction. Finally, metallic sodium may be reacted withchlorodiphenylphosphine (Hewertson, ibid). However,chlorodiphenylphosphine, although commercially available, is somewhatexpensive and is only used because there is little alternative.

There is thus a need for a method of preparing alkali metaldiarylphosphides which is high yielding, uses inexpensive and readilyavailable raw materials and uses what may be termed “conventional”chemical plant.

It has now been surprisingly found that these requirements may be met ifa reaction is carried out between a readily available triarylphosphine,typically triphenyl phosphine, and an alkali metal, typically sodium, ineither a primary aliphatic amine or diamine either alone or diluted witha co-solvent.

According to the present invention there is provided a process forpreparing sodium diaryl salts of phosphides of general formula (I)

R₂P⁻Na⁺  (I)

where R is a phenyl or substituted phenyl group, by reaction of atriarylphosphine with sodium in an aliphatic amine or diamine as solventor co-solvent.

The sodium used in the process of the invention is preferably finelydispersed in a carrier liquid. The liquid carrier may be an inertorganic solvent whose boiling point is above the melting point of sodiumsuch as, for example, toluene, xylene and petroleum ethers.Alternatively, the carrier liquid may be a mineral oil such as, forexample, selected from the Shell Ordina or BP Enerpar range of highgrande mineral oils.

The dispersion of sodium may be prepared by melting sodium metal in thecarrier liquid and stirring rapidly. The sodium in the dispersionpreferably has an average particle size in the range of 0.1 to 1000microns, especially 0.1 to 20 microns. The sodium is preferablydispersed in an amount of 1 g of sodium per 0.1 to 100 cm³, especially0.1 to 5 cm³ of liquid carrier.

A preferred solvent is ethylenediamine. A preferred co-solvent when usedis selected from hydrocarbons and ethers. The hydrocarbon co-solvent maybe aromatic or aliphatic. Toluene is an example of a suitable aromatichydrocarbon co-solvent and hexane is an example of a suitable aliphatichydrocarbon co-solvent. Examples of suitable ether co-solvents for usein the process of the invention include tetrahydrofuran, methy′-butylether and glyme ethers.

The reaction may be carried out in the temperature range of about 0° C.to about 120° C., preferably in the range of 50-70° C.

The sodium diaryl of phosphides prepared according to the invention maybe further treated by reaction with a compound of the general formulaR¹X, where R¹ is selected from hydrogen, phenyl or substituted phenyl(aryl) groups, naphthyl or substituted naphthyl groups, heterocyclicrings, C₁₋₁₀ carbon chains optionally containing branches or unsaturatedlinkages, or —(CR¹R¹)_(n)PRR where n=1 to 10 and X is a suitable leavinggroup, such as halide, methoxide or nitro, to produce phosphines of thegeneral formula.

The reaction temperature for producing unsymmetrical phosphines ispreferably in the range of 0-120° C., especially 20-30° C.

The by-product from this cleavage is phenyl sodium which is a verystrong base. Since this strong base may interfere with subsequentreactions, it is preferable to destroy this reagent before furtherchemistry is carried out. This has been carried out in the literature bythe addition of ammonium salts such as ammonium chloride. In our casethis is not convenient since such ammonium salts are insoluble in thereaction medium. A more convenient method of destruction is by theaddition of an alcohol, such as n-butanol. Although this procedureproduces sodium alkoxides and benzene these by-products do not appear tointerfere with subsequent reactions.

The use of ethylenediamine has a further benefit in the subsequentreaction of the sodium diarylphosphide with a suitable electrophile inthat it is an excellent solvent for conducting such reactions. Thus, thereaction may be brought about by adding the relevant alkyl or activatedaryl halide, either alone or in a suitable co-solvent, to the reactionmixture and heating for an appropriate time to complete the reaction.Work-up of the final product is particularly easy by the cautiousaddition of water to the reaction medium. The solvent, ethylenediamine,and the inorganic by-products are soluble in water and the productsimply precipitates from solution. The product may be isolated in a highdegree of purity by simple filtration, washing and drying.

A particular advantage of the process of the invention is that cryogenicplant is not required and the process is easily operable in standardchemical plant on a large scale. The invention is particularly usefulfor preparing sodium salts of diarylphosphides, especially sodiumdiphenylphosphides, and then further treatment to produce unsymmetricaltriarylphosphides. An advantage of the invention in relation to sodiumsalts is that sodium diphenylphosphide is soluble in the ethylenediaminesolvent and so is tractable in subsequent reactions to give thecorresponding unsymmetrical phosphine.

The invention will now be further described by means of the followingExamples.

EXAMPLE 1 Preparation of Sodium Diphenylphosphide

A dispersion of sodium in mineral oil (25.4 g of 33% w/w dispersion,0.364 mol) was added portionwise over 30 mins to a stirred suspension oftriphenylphosphine (44.0 g, 0.168 mol) in ethylenediamine (50 cm³) undernitrogen at 30° C. On initial addition of the dispersion an immediateexotherm occurred and the reaction mixture turned orange in colour. Onaddition of further portions of the dispersion, the exothermic reactioncaused the internal reaction mixture temperature to rise to 70° C. andthe reaction mixture to turn deep red in colour. Upon completion ofdispersion addition the reaction mixture was stirred for a further 1 to2 hours at 50-70° C. to ensure completion of reaction to afford a thick,deep red mobile reaction mixture containing sodium diphenylphosphide andphenyl sodium. The reaction mixture was then treated dropwise withbutanol (12.0 g) at 50° C. to destroy phenyl sodium and stirred at40-50° C. for a further hour. The reaction mixture produced in this waymay be used directly in further reactions without any further treatment.

EXAMPLE 2 Preparation of 2-(Diphenylphosphino) Pyridine

A solution of 2-chloropyridine (19.0 g, 0.167 mol) in toluene was addeddropwise to the material produced in Example 1 at 15-25° C. over 30mins. The resulting exotherm was controlled by means of an ice bath. Thecolour of the reaction first turned dark brown before turning beige. Oncompletion of the reaction, the mixture was stirred for a further 30mins to ensure completion of reaction. Water (150 cm³) was thencautiously added to afford a creamy yellow reaction mixture. The mixturewas cooled to 0-5° C. and then filtered, washed with water and dried.The product was obtained as a cream coloured solid which was fairlypure. Yield=31.0 g (70% based on triphenylphosphine).

EXAMPLE 3 Preparation of Sodium Diphenylphosphide

In this Example a co-solvent is used in the process.

A dispersion of sodium in mineral oil (25.4 g of 33% w/w dispersion,0.364 mol was added portionwise over 30 mins to a stirred suspension oftriphenylphosphine (44.0 g, 0.168 mol) in ethylenediamine (90 cm³) andtoluene (30 cm³) under nitrogen at 30° C. On initial addition of thedispersion an immediate exotherm occurred and the mixture turned orangein colour. On addition of further portions of the dispersion, theexothermic reaction caused the internal reaction mixture temperature torise to 70° C. and the reaction mixture turn deep red in colour. Uponcompletion of dispersion addition the reaction mixture was stirred for afurther 1 to 2 hours at 50-70° C. to ensure completion of reaction, toafford a thin deep red mobile reaction mixture containing sodiumdiphenylphosphide and phenyl sodium. The reaction mixture was thentreated with butanol (12.0 g) at 50° C. to quench phenyl sodium andstirred at 40-50° C. for a further hour. The reaction mixture producedin this way may be reacted with compounds of the general formula R¹X toprepare unsymmetrical phosphines in good yield without any furthertreatment.

EXAMPLE 4 Preparation of Sodium Diphenylphosphide

In this Example the mode of reagent addition is reversed and aco-solvent is used.

Thus ethylenediamine (90 cm³) was added dropwise over 30 mins to astirred suspension of a dispersion of sodium in mineral oil (25.4 g of33% w/w dispersion, 0.364 mol), triphenylphosphine (44.0 g, 0.168 mol)and methyl¹-butyl ether (30 cm³) under nitrogen at 30° C. On initialaddition ethylenediamine an immediate exotherm occurred and the mixtureturned orange in colour. On addition of further portions ofethylenediamine, the exothermic reaction caused the internal reactionmixture temperature to rise to 70° C. and the reaction mixture turn deepred in colour. Upon completion of ethylenediamine addition the reactionmixture was stirred for a further 1 to 2 hours at 50-70° C. to ensurecompletion of reaction, to afford a deep red mobile reaction mixturecontaining sodium diphenylphosphide and phenyl sodium. The reactionmixture was then treated with butanol (12.0 g) at 50° C. to quenchphenyl sodium and stirred at 40-50° C. for a further hour. The reactionmixture produced in this way may be reacted with compounds of thegeneral formula R¹X to prepare unsymmetrical phosphines in good yieldwithout any further treatment.

What is claimed is:
 1. A process for preparing alkali metal diarylphosphides of general formula (I) R₂P⁻Na⁺  (I) where R is a phenyl orsubstituted phenyl group, by reaction of the correspondingtriarylphosphine with sodium in an aliphatic amine or diamine as solventor co-solvent.
 2. A process as claimed in claim 1, wherein the sodium isfinely dispersed in a carrier liquid.
 3. A process as claimed in claim2, wherein the carrier liquid is an inert organic solvent whose boilingpoint is above the melting point of sodium.
 4. A process as claimed inclaim 2, wherein the carrier liquid is selected from toluene, xylene andpetroleum ethers.
 5. A process as claimed in claim 2, wherein the liquidcarrier is a mineral oil.
 6. A process as claimed in claim 2, whereinthe dispersion of sodium is made by melting sodium metal in the carrierliquid and stirring rapidly.
 7. A process as claimed claim 2, whereinthe sodium has an average particle size in the range of 0.1 to 1000microns.
 8. A process as claimed in claim 7, wherein the sodium has anaverage particle size of 0.1 to 20 microns.
 9. A process as claimed inclaim 2, wherein the sodium is dispersed in an amount of from 1 g ofsodium per 0.1 to 100 cm³ of liquid.
 10. A process as claimed in claim9, wherein the sodium is dispersed in an amount of 1 g of sodium per 0.1to 5 cm³ of liquid carrier.
 11. A process as claimed in claim 1, whereinthe aliphatic diamine is ethylenediamine.
 12. A process as claimed inclaim 1, wherein the diamine is diluted with a co-solvent.
 13. A processas claimed in claim 12, wherein the co-solvent is selected fromhydrocarbons and ethers.
 14. A process as claimed in claim 13, whereinthe hydrocarbon co-solvent is aromatic.
 15. A process as claimed inclaim 14, wherein the aromatic hydrocarbon is toluene.
 16. A process asclaimed in claim 15, wherein the hydrocarbon co-solvent is an aliphatichydrocarbon.
 17. A process as claimed in claim 16, wherein the aliphaticco-solvent is hexane.
 18. A process as claimed in claim 13 where theether co-solvent is selected from tetrahydrofuran, methyl-butyl etherand glyme ethers.
 19. A process as claimed in claim 1, wherein thereaction temperature is in the range of 0-120° C.
 20. A process asclaimed in claim 19, wherein the reaction temperature is in the range of50-70° C.
 21. A process as claimed in claim 1 including the step ofadding an alcohol to the reaction medium after formation of the sodiumdiarylphosphide.
 22. A process as claimed in claim 21, wherein thealcohol is n-butanol.
 23. A process as claimed in claim 1, wherein thetriarylphosphine is triphenylphosphine.
 24. A process for preparing anunsymmetrical phosphine comprising reacting a sodium diarylphosphideprepared by the process of claim 1 with a compound of the generalformula R¹X, where R¹ is selected from the group consisting of hydrogen,phenyl, substituted phenyl, naphthyl, substituted naphthyl, heterocyclicrings, and C₁₋₁₀ carbon chains and X is a suitable leaving group.
 25. Aprocess as claimed in claim 24, wherein in the formula R¹X, X isselected from the group consisting of halide, methoxide and nitrogroups.
 26. A process as claimed in claim 24, wherein the reactiontemperature is in the range 0-120° C.
 27. A process as claimed in claim26, wherein the reaction temperature is in the range 20-30° C.
 28. Aprocess as claimed in claim 24, wherein the C₁₋₁₀ carbon chains containa functionality selected from the group consisting of a branched chain,an unsaturated linkage, and combinations thereof.
 29. A process forpreparing alkali metal diaryl phosphides of general formula (I)R₂P⁻Na⁺  (I) where R is a phenyl or substituted phenyl group, byreaction of the corresponding triarylphosphine with finely dispersedsodium in an aliphatic amine or diamine as solvent or co-solvent.
 30. Aprocess as claimed in claim 29, wherein the dispersion of sodium is madeby melting sodium metal in the carrier liquid and stirring rapidly. 31.A process as claimed in claim 29, wherein the sodium has an averageparticle size in the range of 0.1 to 1000 microns.
 32. A process asclaimed in claim 31, wherein the sodium has an average particle size of0.1 to 20 microns.